The present invention relates generally to the manufacture of carbon/carbon parts, and more particularly to a needled, fibrous preform that is compacted during carbonization.
Carbon/carbon parts (“C/C”) in the form of friction disks are commonly used for aircraft brake disks and race car brake and clutch disks. Carbon/carbon brake disks are especially useful in these applications because of the superior high temperature characteristics of C/C material. In particular, the carbon/carbon material used in C/C parts is a good conductor of heat and is able to dissipate heat generated during braking away from the braking surfaces. Carbon/carbon material is also highly resistant to heat damage, and thus, is capable of sustaining friction between brake surfaces during severe braking without a significant reduction in the friction coefficient or mechanical failure.
In general, there are currently two primary methods of manufacturing C/C materials. The first method involves the layup and cure of a carbon fiber, phenolic resin matrix composite, followed by pyrolysis and subsequent phenolic resin infiltration and pyrolysis cycles. Multiple resin infiltration and pyrolysis cycles are typically used until the part achieves the desired density. The second method involves fabrication of an oxidized PAN or carbon fiber preform, followed by carbonization and chemical vapor infiltration (CVI) densification. The chemical vapor infiltration cycles are continued, in conjunction with machining the preform between infiltration cycles if desired, until the desired part density is achieved. Combinations of these two basic process methods are also in use and may include variations in preform architecture, infiltration resin type, and chemical vapor infiltration conditions.
In general, C/C parts produced using the oxidized PAN fiber, carbonization, and CVI densification method are made in three successive manufacturing steps. First, a fibrous preform is made utilizing a variety of textile manufacturing techniques. Typically, the fibrous preform is made from oxidized polyacrylonitrile (PAN) fiber (“OPF”). Although numerous techniques are known in the art for making fibrous preforms from OPF, a common technique involves stacking layers of OPF to superimpose the layers. The added layers may then be needled perpendicularly to the layers with barbed, textile needles. The needing process generates a series of z-fibers through the fibrous preform that extend perpendicularly to the fibrous layers. The z-fibers are generated through the action of the needles pushing fibers from within the layer (x-y or in-plane) and reorienting them in the z-direction (through-thickness). Needling of the fibrous preform may be done as one or more layers are added to the stack or may be done after the entire stack is formed. The needles may also penetrate through only a portion of the preform or may penetrate through the entire preform. In addition, resins are sometimes added to the fibrous preform by either injecting the resin into the preform following construction or coating the fibers or layers prior to forming the fibrous preform.
After the fibrous preform is made, it is carbonized to convert the OPF into carbon fibers. Typically, fibrous preforms are carbonized by placing the preforms in a furnace with an inert atmosphere. As well-understood by those in the art, the heat of the furnace causes a chemical conversion which drives off the non-carbon chemicals from the preform. The resulting preform generally has the same fibrous structure as the fibrous preform before carbonizing. However, the OPF have been converted preferably to almost 100% carbon.
After the preform has been carbonized, the preform is densified. In general, densification involves filling the voids, or pores, of the fibrous preform with additional carbon material. This may be done using the same furnace used for carbonization or a different furnace. Typically, chemical vapor infiltration and deposition (“CVI/CVD”) techniques are used to densify the porous fibrous preform with a carbon matrix. This commonly involves heating the furnace and the carbonized preforms, and flowing hydrocarbon gases into the furnace and around and through the fibrous preforms. As a result, carbon from the hydrocarbon gases separates from the gases and is deposited on and within the fibrous preforms. When the densification step is completed, the resulting C/C part has a carbon fiber structure with a carbon matrix infiltrating the fiber structure, thereby deriving the name “carbon/carbon”.